A network printer connected directly to a LAN or other network is equipped with a function that follows the recommendations of the document printing architecture, or DPA. For this type of printer, it is possible to cancel a print job already inside the printer, to list information about a job, to change the output priority of the job, and so forth, all from a terminal on the network. Additionally, printing systems that make it possible to control a network printer are now commercially available. Such printing systems provide functions that are called from a user application, as a result of which the printer can be used more easily.
Ordinarily, a network printer is provided with a LAN interface card called a network interface card, or NIC, through which output images are sent to a controller inside the printer. If an instruction is issued from a user application to cancel a print job after the job has been sent to the printer from the user application via the printing system, the printing system executes a cancellation of the job using a predetermined procedure.
In addition to handing over the print job issued from the application to the printer, the printing system also tracks which print jobs are currently being processed by the printer and which jobs are in the queue for printing. In addition to the cancellation described above, the printing system can also perform a variety of control operations, such as upon request outputting the printer status to the application and changing the order in which the print jobs are processed.
However, current printing systems described above have several disadvantages, as described below.
For example, even when a print job is entered into the printer from the application program via the printing system, it can happen that the particular job in question is not stored in the job management area inside the printer because the upper limit on the number of jobs that the printer can hold at one time has been exceeded. Jobs that are not stored in the printer's management area cannot be seen from the printing system, either, and as a result, such a print job cannot be cancelled.
In such a case, the printing system must respond promptly to a job cancel request from the upstream application, because unless the printing system does respond to such a request the system may shut down in the interim. As a result, the printing system fails to cancel the designated print job and answers the application with an error code indicating that the job cancel has failed. Or, the printing system executes a soft reset of the printer—while running the risk of deleting other print jobs as well—and answers the application with a cancel succeed return code. In either case, the cancellation is not only not certain, but, depending on the method employed, there is a possibility that jobs other than the designated one will be canceled instead.